1. Field of the Invention
This invention relates to an improved lubricating oil composition having a substantially reduced pour point. More particularly, this invention relates to an improved lubricating oil composition comprising a paraffinic waxy-type, residual lubricating oil base stock and from about 0.01 to about 0.50 weight percent of an oil-soluble copolymer of ethylene and a vinyl ester of a lower saturated monobasic aliphatic carboxylic acid.
2. Description of the Prior Art
Heating oils, diesel fuels, lubricating oils and other liquid hydrocarbon oils employed in cold climates or exposed to low temperatures frequently require the use of an additive to maintain their fluidity or to meet critical pour point specifications for the oil in question. Additives that are effective for this are called pour depressants. The art discloses numerous classes of pour depressants.
Such lubricating oil additives are mostly high molecular weight organic compositions prepared by alkylation of benzene, naphthalene or derivatives, by polymerization of low molecular weight methacrylates or by condensation polymerization of various types. Many are not entirely suitable because of their high cost, or the high concentration required, or because they do not lower the pour point to the required temperature. An effective pour depressant is one which will substantially reduce the pour point of a treated oil when used in small concentration without imparting any undesirable effects.
Although the wide variety of differeent pour depressants mentioned above are useful for incorporating in heating oils, diesel fuels and many other liquid hydrocarbon oils, it has been found that such additives are generally ineffective in paraffinic, waxy-type, residual lubricating oil base stocks. The poor performance of these additives may result from the structural differences of waxes occurring in lubricating oils derived from different locations. It is well known, for example, that acrylate and methacrylate esters of aliphatic acids having eight carbon atoms or more can be polymerized to make high molecular weight products which are soluble in lubricating oils and generally are capable of improving or lowering the pour points of a variety of lubricating oils. With the paraffinic, waxy-type, residual lubricating oil base stocks these materials do not provide the pour point reductions required.
Two principal processes have been employed in attempting to improve the pour point characteristics of paraffinic, waxy-type, residual lubricating oil base stocks, namely, the solvent extraction process and the centrifugal dewaxing method. Solvent dewaxing involves introducing and recovering a largee amount of valuable solvent material which necessarily results in an expensive operation. In the centrifugal method of separating the wax, it is necessary to first cool the oil to a low temperature such as about -25.degree.F, which is a time-consuming and costly processing step.
Another approach which has been employed has been to dilute or cut the lubricating oil stock with a major amount of a lighter hydrocarbon oil. Thermocracking of the waxy lubricating oil base stock has been attempted; however, this process which does result in the reduction of the pour point to 10.degree.-20.degree.F also leads to the loss of a substantial volume of lubricating oil stock due to poor selectivity in cracking the wax that causes the high pour point. There is, therefore, a need in the art for an economic process to form improved lubricating oil compositions utilizing as the major component paraffinic, waxy-type, residual lubricating oil base stocks.
A main object of the present invention is to improve the pour point characteristics of paraffinic, waxy-type, residual lubricating oil base stocks without using elaborate and expensive solvent extraction or centrifugal dewaxing procedures.
Another object of this invention is to provide improved lubricating oil compositions prepared by incorporating a minor amount of an oil-soluble copolymer of ethylene and a vinyl ester of a saturated monobasic aliphatic monocarboxylic acid in a paraffinic, waxy-type residual lubricating oil base stock.
Another object of this invention is to improve the paraffinic, waxy-type, residual lubricating oil base stocks so that they may be handled with greater ease and flexibility in climates where the ambient temperatures are near their upper pour points.